Approximately 5 million patients in the United States have heart failure and over 500,000 new patients are diagnosed each year. Individuals with the most advanced stage of heart failure do not respond to optimal medical therapy. The purpose of this discovery R21 application is to identify a new class of regulatory mutations in individuals with heart failure using an innovative approach to map single nucleotide polymorphisms (SNPs) that disrupt microRNA (miRNA) binding sites. These SNPs may inhibit miRNA binding or create new miRNA binding sites. The hypothesis to be tested is that SNPs in miRNA binding sites of genes that regulate myocyte contractility and relaxation are associated with increased risk of early onset dilated cardiomyopathy and advanced heart failure. These experiments leverage a unique resource of banked and fresh human tissue from patients receiving a ventricular assist device (VAD) or heart transplant. A strength of this strategy is the high probability of simultaneously identifying the biological mechanism through which the identified SNPs influence genetic risk. Access to newly procured human tissue permits measurements of myocyte contractility. We propose the following specific aims: Specific Aim I. Identify new SNP associations in miRNA binding sites of genes associated with sarcomere function and calcium handling in individuals with early onset dilated cardiomyopathy and advanced heart failure. Specific Aim II. Identify the role of SNPs in miRNA binding sites of genes associated with sarcomere function and calcium handling on myocyte contractility and relaxation in isolated cardiac myocytes from core biopsies. PUBLIC HEALTH RELEVANCE: Experiments outlined in this proposal will test an innovative approach to identify a new class of regulatory mutations in microRNA binding sites in individuals with heart failure. These mutations may disrupt microRNA binding or create new microRNA binding sites.